Church leaders asking people to join in praying for peace in Ukraine after Russia sent troops into the country leading to reports of explosions near major cities.
There were long tailbacks on roads out of capital city Kyiv on Thursday morning as people tried to flee.
Pope Francis spoke of the "great pain in my heart" as he declared 2 March - Ash Wednesday - a second day of prayer and fasting for Ukraine.
"Despite the diplomatic efforts of the last few weeks, increasingly alarming scenarios are opening up," he said during Wednesday's General Audience.
"Once again the peace of all is threatened by partisan interests."
The Pope called on political leaders to show restraint and to refrain from doing anything that would bring more suffering to people or destabilize the peaceful coexistence of nations.
He urged those "with political responsibility to examine their consciences seriously before God, who is the God of peace and not of war, who is the Father of all, not just of some, who wants us to be brothers and not enemies".
The Archbishops of Canterbury and York have issued a special prayer to be used for Ukraine in which they pray for peace and the laying down of weapons:
God of peace and justice,
We pray for the people of Ukraine today.
We pray for peace and the laying down of weapons.
We pray for all those who fear for tomorrow,
that your Spirit of comfort would draw near to them.
We pray for those with power over war or peace,
for wisdom, discernment and compassion
to guide their decisions.
Above all, we pray for all your precious children, at risk and in fear,
that you would hold and protect them.
We pray in the name of Jesus, the Prince of Peace.